2aSA3. Accuracy of dynamic modulus measurements made with the dynamic
mechanical thermal analyzer.

The accurate determination of the complex moduli of viscoelastic materials
is of great importance for the efficient design of many noise control devices.
It is often the case that a design, in conjunction with its acoustic
performance requirements, leads to a narrow band of acceptable dynamic modulus
for the viscoelastic material. In such cases knowledge of the accuracy and
reliability of the measurement apparatus is essential. Dynamic complex shear
modulus is measured at Carderock Division Naval Surface Warfare Center (CDNSWC)
with the Dynamic Mechanical Thermal Analyzer (DMTA), manufactured by Polymer
Laboratories. An attempt to quantify the absolute accuracy of the DMTA
measurement has been made through the consideration of errors including the
accuracy of the beam solution used to infer the complex modulus, compliance of
the sample mounts, measurement noise, temperature control, thermal stress,
Poisson effects, and the implementation of time-temperature superposition. With
these considerations, an ad hoc error analysis is implemented to quantify
absolute error bounds expected for DMTA measurements of a hypothetical
material. These results are of direct interest to the ASA Committee on
Standards S2WG79, ``Characterization of the Dynamic Properties of Viscoelastic
Polymers,'' which has initiated round-robin testing among committee
participants. CDNSWC results from the DMTA tests of three round-robin materials
will be presented.